Blending method and apparatus



Sept. 20, 1955 L. F. SAMLER 2,718,471

BLENDING METHOD AND APPARATUS Filed Aug. 1, 1952 INVENTOR BY w ELOQKSATTORNEY United States Patent BLENDIN G METHOD AND APPARATUS Lee E.Samler, Baltimore, Md., assignor to The National Plastic ProductsCompany, Odeuton, Md, a corporation of Maryland Application August'l,1952, Serial No. 302,092

16 Claims. (Cl. 106-181) The present invention relates to the treatmentof solid materials in particle form and more particularly to a methodand apparatus for adding a fluid material to a powdered or granularmaterial to obtain a uniform dispersion of the fluid in the solidmaterial.

This case is a continuation-in-part of copending case Serial No. 1 77,670, filed August 4, 1950, now abandoned, entitled Blending Method andApparatus.

In many processes it is necessary tocondition solid materials which arein particle form by the addition of treating agents inv fluid formwherein. it is essential: that the agents be uniformly distributed inthe solid particles. This; is particularly difficult to. accomplish whenthe amount of agent tobe added is relatively smallas compared tofthequantity of solid particles in which it is to be distributed.

' In accordance with methods heretofore employed for this purpose, thematerial in particle form is dissolved ina suitable solvent to whichthefluid: material is added in form. The materials are suitably blended. invari-- oua ways during or after which the solvent is evaporated. Theresultant material is then mechanically disintegrated to'for'mv thesolid material again in particle form. in which. the; fluid isunifiormly dispersed. This method is relatively slow and expensive and.requires the use of machinery which is: heavy and expensive in relationto: its. capacity to produce finished material. Further, such a process:cannot be successfully employed with heat-sensiflivematerials due to thedegradation of the product be: causeof the relatively high temperaturesto which the ma terial must. be subjected during; the processing.

-It has also been heretofore proposed to: eflect the in- Corporation of.the fluid by what may be termed an essentially dry process in which themass of powdered material insubstantially dry state is agitated while.the fluid material is added. One method which has been proposed was totumble the mass of particles in a closed rotary tumbling vessel and tointroducethe liquid by pouring or spraying, depending upon the tumblingaction to: dis persed the liquid uniformly. It has been diflicult by'this method to achieve uniformly satisfactory dispersion of the liquidin the solid mass.

The general object of the present invention is to provide a new andimproved method and apparatus for incorporating a fluid into a mass ofsolid particles in such manner as to obtain a uniform dispersion of thefluid in the solid particles.

. A further object of the invention is to provide a method and apparatusfor incorporating a liquid into a mass of solid particles'whilemaintained essentially dry in such a manner as to obtain a uniformdispersion of the fluid in the solid particles.

A still further object of the invention is to provide a method andapparatus for dispersing a fluid in a mass of solid particleswherein thefluid is brought into contact with the individual particles of the solidmass while the particles are in suspension in a gas.

A still further object of the invention is to provide a "ice 2, methodand apparatus for uniformly dispersing a liquid additive in a finelydivided thermoplastic material.

Other objects and the nature and advantages of the instant. inventionwill be apparent from the following description taken in conjunctionwith the accompanying drawing, wherein:

Fig. l is a sectional view illustrating apparatus capable of carryingthe invention into effect, and

Fig. 2 is an enlarged detail partly broken away of the mixer in theliquid tank.

Although the present invention has many applications, it will bespecifically described for the addition of various agents tothermoplastic compounds in particle form. The agents to be added areusually in liquid form such as, for example, plasticizers, stabilizers,pigments, dyes, and the like. The agents, if not liquids, can be eitherdissolved or dispersed inliquid prior to introduction into the polymer.

This invention is of particular value in the treatment of heat-sensitivematerials, such as vinyli'dene chloride resins, where it is necessary toeliminate such operations as hot milling for blending the plasticizerinto the polymer, although it is equally applicable to the incorporationof. additivesto any thermoplastic material.

The incorporation of pigments into vinylidene chloride resins. has beena particularly difficult problem. It has been the practice to pigmentvinylidene chloride resins by using dry pigments that have beenhammer-milled or processed: inv other types of dry grinding equipment.The ground pigment is then dry blended with the polymer in suchequipment as double conical blenders, ribbon mixers and the like. Thisprocedure does not give a uniform dispersion because: the pigmentparticle size varies over a very wide range; if the pigment particlespick up a like static charge to the polymer particles, they repel oneanother; and at best, there is only a mechanical mixture of widelyvarying size and gravity of materials that, upon vibration attendant tosubsequent handling, will separate and form striations.

- In accordance with the present invention, the solid particles aresuspended in a gas moving at a high velocity. The liquid to be dispersedtherein, which may include plasticizers, stabilizers, pigments, dyes,and the like in solution or suspension, is sprayed into the movingsuspended particles in suchv a manner that the liquid comes in contactwith individual particles of the solid; and further, the ratev of flowof the solid particles and the liquid can be. so; metered that the solidcan be recycled several times before the total quantity of liquid hasbeen injected into the system, thus insuring a uniform dispersion.

It is of particular importance in the coloring of thermoplasticmaterialsv which are to be extruded into filaments, that the pigmentparticle size be extremely small. If large size pigment particles appearin the final filament, the filament is weakened at that point. If thepigment is purchased having the proper particle size in pulp form, thatis, suspended in a liquid, the liquid is removed and the pigment can bedispersed in the plasticizer. If the pigment is purchased in the usualdry form, it must be ground to an average particle size of one micron.This is accomplished by grinding the pigment in a portion of theplasticizer in. a ball mill or a similar type grinding machine. Theparticle size can be better controlled with a more uniform product thancan be achieved by dry grinding. Pigments in this form can then bedissolved or dispersed in the total quantity of plasticizer prior to theintroduction of the plasticizer to the polymer. By this procedure, eachindividual particle of the polymer will be dyed and subsequentseparation and striations are avoided.

In the. introduction of either powdered or liquid stabilizers, or otheradditives the same method would apply as for pigmentation.

Referring to Figure l, apparatus is shown which is suitable for carryingout the process described. The main hopper is supported on a framework11 at a suitable height from the ground. The upper end of the hopper isprovided with a hinged cover 12 having a loading hatch 12 through whichthe solid granular material is loaded into the hopper. The lower portion13 of the hopper which is of frusto-conical shape is provided with ajacket 13' which surrounds the hopper. The bottom of the hopper isprovided with an opening 14 which communicates with a horizontal sleeve15.near an end thereof that is closed. A vibrator 16 is attached to theouter side of the portion 13 of hopper 10 to prevent the particles fromadhering to the hopper walls. A feed metering screw 17 operating in thesleeve is driven by a belt 18 connected to a variable speed driveillustrated at 19.

Near the open discharge end of the sleeve 15 is an opening 20 in thelower surface of the sleeve closed by a sliding valve 21. Aligned withthe opening 20 is a discharge spout 22 for removing the contents of thehopper when the operation has been completed. The open end of the sleeve15 connects with a tube 23 which curves upwardly and discharges into thetop of the hopper 10 against a baffie 23'. The tube 23 is supported bysupports 24 and 25 which are attached to the framework 11.

A liquid tank 26 is supported by the framework 11 below the hopper 15.The tank 26 is connected to a fluid metering pump 27 by a conduit 28. Aconduit 29 connects the pump outlet with a nozzle 30 which is locatedwithin the tube 23. The pump pressure is controlled by means of a bypass31 connecting the outlet side of the pump with the intake side. A gage32 and valve 33 are provided in the bypass line 31. The pump 27 isdriven by a motor 34. Conduit 29 enters the conveying tube 23 through anelbow 35 and extends concentrically with the tube 23 to the nozzle 30.

Extending into the hopper 10 supported at the top is a vertical sleeveopen at the bottom and provided with a plurality of openings 41 at theupper end thereof. Immediately below the openings 41, a conical bafile42 is secured to the outer wall of the sleeve 40 tapering outwardly atthe lower end thereof. A screw conveyor 43 is located within the sleeve40, and is driven by a variable speed drive 44 mounted above the hopper10. The tube 23 empties into the upper end of the hopper 10 at a pointdirectly above the baflie 42 adjacent the openings 41 in the sleeve 40.

An upwardly inclined outlet 45 for the conveying gas from the tube 23 isprovided at the upper end of the hopper 10 at the opposite side from thepoint at which the tube 23 enters the hopper. An upwardly inclinedfilter housing 46 is connected to the outlet 45 and surrounds a filterbag 47. A vibrator 47' attached to the housing 46 vibrates the filterbag and thus returns the particles of solid material collecting thereinto the hopper 10. A conduit 48 connects the filter housing with a blower49, and conduit connects the outlet from blower 49 with heat exchanger51. Conduit 52 connects the heat exchanger outlet with the horizontalsleeve 15 near the outlet thereof at point to supply the gas at theproper temperature and velocity in which the solid particles aresuspended.

The tube 23 is preferably made of stainless steel with a portion made ofglass for purposes of visibility although any suitable material may beused.

When the apparatus is utilized for the absorption of a plasticizer by athermoplastic material, it has been found essential to maintain anelevated temperature, the temperature range depending upon thethermoplastic material and its thermal stability as well as the boilingpoint of the plasticizer. In general, a temperature range ofapproximately l250 F. is satisfactory. Further, it is necessary thatthis temperature be accurately controlled. 7

To accomplish this purpose, the present invention includes the jacket13' surrounding the hopper 13. A heat transfer fluid is circulatedthrough the jacket 13' entering at inlet 55 and leaving at outlet 56.The fluid may be hot water or any other suitable medium for quicklybringing the particles in the hopper to the proper temperature.

The heat exchanger 51 is utilized to control the temperature of theconveying gas. At the beginning of the operation, the gas is heated tothe desired temperature. However, after the gas has passed through theblower several times, the temperature of the gas may increase to thepoint that the heat exchanger 51 must be used to cool the gas down tothe desired temperature. The control of the heating medium and thecooling medium to the heat exchanger can be accomplished by use of athree-way modulating or proportioning valve.

The material in the liquid tank 26 is constantly agitated by means of amixer 57 driven by a motor 58. The use of the mixer 57 prevents theprecipitation of any solids incorporated in the liquid in the tank 26. Amixerwhich has been found particularly suitable for this purpose is theEppenbach Homo-Mixer, described in United States Patent No. 2,393,360.

The gas used as the conveying gas should preferably be inert. Nitrogenhas been found to be particularly suitable. One advantage of the use ofan inert gas is to exclude oxygen, thereby preventing oxidation of thepolymer and thus removing the combustion hazard.

The operation of the system in general is as folows: The system is firstpurged of air by flowing an inert gas thereinto. The powdered orgranular thermoplastic material is loaded into the hopper. Preferablythe hopper is not loaded to more than 50% of total hopper volume forbest results. The heating medium is passed through the hopper jacket13'. The two screw conveyors 17 and 43 and the mixer 57 are started inoperation as well as the blower 49 and the pump 27. The gas iscompressed in the blower 49, passed through heat exchanger 51 and thenceis injected into the particles of thermoplastic material beingdischarged from the hopper 10 through the sleeve 15 at point 55 by meansof the screw conveyor 17. The gas which has been heated to the desiredtemperature in the heat exchanger 51 and injected into the outlet ofsleeve 15 picks up the solid particles likewise at the desiredtemperature and conveys them in fluid suspension into the tube 23.Liquid from the tank 26 is pumped at the desired rate and dischargedthrough the spray nozzle 30 into the moving gas suspension whereupon theliquid contacts the individual particles and is absorbed by them. Thegas suspension is conducted via tube 23 to the upper end of the hopper10 and contacts bafiie 23' where, due to decreasing velocities, thesolid particles drop out of gas suspension. The gas, which probablycontains some volatile material as well as some of the solid material,is recycled through the filter bag 47, blower 49 and heat exchanger 51.The material in the hopper 10 is continuously intermixed by means of thescrew conveyor 43 which picks up material from an intermediate portionof the hopper and discharges it through the openings 41 at the top ofthe vertical sleeve 40. The treated material returning from tube 23 isbrought into contact with the untreated material flowing through theopenings 41.

The rates of feed of the liquid and the solid particles are adjusted sothat the solid particles will have been recycled at least two timesbefore the total amount of liquid has been introduced. After the liquidhas all been added and sufficient recycling has been carried on toinsure complete absorption of the liquid by the particles, the treatedsolid particles are then discharged by opening the slide valve 21 andconveying the particles through opening 20 and discharge spout 22.

The particles suspended in the gas are caused to move at highvelocities, preferably from 1500 to 4000 feet per minute. The bend inthe tube 23 produces extreme turbulence which causes any formedagglomerates to break up and further disperse. 4

The following specific examples are intended to illustrate the presentinvention but are not intended to limit the same:

Example I After the air has been purged from the apparatus by flowingnitrogen through the system,- 1000 pounds of powdered vinylidenechloride-vinyl chloride co-polymer' is added to the hopper. Theparticles of the material are of such a size that 2% or less by weightare left on a twenty mesh screen. The resin is heated by the hopperheating jacket 13' to approximately 90 C. The nitro* gen gas is likewiseheated inthe heat exchanger 51 to approximately 100-110 C. The liquidinthe tank 26 comprises a combination of a plasticizer, stabilizer and apigment. The pigment particles have an average par ticle 'size of onemic'r'on. As a plasticizer, any one or combination of the following canbe ii'sed, dioctyl phthalate, dimethyl phthalate, diethyl phthalate,diallyl phthalate, dioctyl adipate, dioctyl sebacate, methyl phthalylethyl glycollate, triphenyl phosphate or poylmeric polyester types ofplasticizers. As a stabilizer any suitable organic or inorganicstabilizer may be used. In the present example, dibasic lead sulphate isused. Any suitable pigment can be utilized depending on the colordesired, as for example, bluecopper phthalocyanine, White-titaniumdioxide, and black-carbon black. The following proportions of theadditives are used:

Plasticizer 8-10% of weight of resin. Stabilizer 0.5-3% of weight ofresin. Pigment Up to 1% of weight of product.

The liquid is pumped in at such a rate that the resin is recycled twicewhile the liquid is being sprayed in. The treated resin is recycled oncemore after completion of the addition of liquid. The gas with theparticles suspended therein is moved through the system at a velocity ofabout 4000 feet per minute.

Example II The hopper is loaded with cellulose acetate flake untilaproximately one-half full. The tank 26 is filled with a liquidplasticizer comprising equal parts diethyl phthalate and dimethylphthalate. The relative quantities of resin and plasticizer are in theratio of 70 parts resin to parts plasticizer. Nitrogen is utilized asthe inert gas and the process described in Example I is utilized.

Example III Parts Vinyl chloride-vinyl acetate copolymer 100 Dioctylphthalate 30 Lead stear 0.3

Dibasic lead phosphate 1.5

The process of Example I is utilized, and the resultant product is afinely divided, uniformly plasticized and stabilized vinylchloride-vinyl acetate copolymer.

The method described is essentially a dry method which maintains theparticle mass in free-flowing condition during the process. To this end,the rate of introduction of the liquid into the tube 23 must becontrolled as to rate and manner of introduction so as to avoidappreciable Wetting of the wall of the tube since if that occursagglomeration or lumping of the particle material ensues.

As will be apparent from the foregoing description, the invention in itsseveral aspects has a Wide field of utility applicable to many differentspecific materials and combinations thereof to produce many diiferentkinds of desired end products. V A v It will likewise be obvious tothose skilled in the art that various changes may be made Withoutdeparting from the spirit of the invention and therefore the inventionis not limited to what is shown in the drawings and described in thespecification but only as indicated in the-appended claims.

I claim: I

l. The method of plasticizing a mass of finely divided thermoplasticmaterial which includes the steps of continuously removing particles ofthe thermoplastic mate! rial from the mass, suspending the particles ina rapidly moving inert gaseous medium, gradually spraying theplasticizer into the suspended particles of thermoplastic material,separating the treated particles from the gaseous medium and returningthe treated particles to the mass 2. The method in accordance with claim1, wherein the plasticizer has incorporated therewith a stabilizer andapigment. v

3. The method of plasticizing a mass of thermoplastic material particleform which includes the steps of com tinuously removing particles of thethermoplastic material from the mass, suspending the particles in arapidly moving inert gaseous medium, spraying the plasticizer into thesuspended particles, separating the treated particles from the gaseousmedium and returning the treated particles to the mass for recycling,recycling the treated particles at least two times before the totalamount of plasticizer has been added to the suspended particles.

4. The method in accordance with claim 1 wherein the temperature of themass of particles and of the gaseous medium is maintained relativelyconstant during the process.

5. The method in accordance with claim 1 wherein the inert gaseousmedium used is nitrogen.

6. The method in accordance with claim 1 wherein particles ofthermoplastic material are continuously removed from the mass andbrought into contact with the treated particles being returned to themass.

7. The method of plasticizing a mass of thermoplastic material inparticle form which includes the steps of continuously removingparticles from the bottom portion of the mass, suspending the particlesin a rapidly moving inert gaseous medium, gradually spraying theplasticizer into the suspended particles, separating the treatedparticles from the gaseous medium, returning the treated particles tothe upper portion of the mass, continuously removing particles from anintermediate portion of the mass, and bringing the particles from theintermediate portion of the mass into contact with the treated particlesbeing returned to the upper portion of the mass.

8. The method in accordance with claim 7, wherein the temperature of themass of particles and of the gaseous medium is maintained relativelyconstant during the process.

9. The method in accordance with claim 7, wherein the gaseous mediumseparated from the treated particles is filtered, pumped, passed in heatexchange relation and thence recycled to the system.

10. The method of plasticizing a mass of thermoplastic material inparticle form which includes the steps of continuously removingparticles from the bottom portion of the mass, suspending the particlesin a rapidly moving inert gaseous medium, gradually spraying theplasticizer into the suspended particles, separating the treatedparticles from the gaseous medium, returning the treated particles tothe upper portion of the mass for recycling, continuously removingparticles from an intermediate portion of the mass, and bringing theparticles from the intermediate portion of the mass into contact withthe treated particles being returned to the upper portion of the massfor recycling, recycling the treated particles at least two times beforethe total amount of plasticizer has been added to the suspendedparticles.

11. The method in accordance with claim 1, wherein the thermoplasticmaterial is a vinylidene chloride-vinyl chloride copolymer.

12. The method in accordance with claim 1, wherein the thermoplasticmaterial is cellulose acetate and the plasticizer is a mixture of equalparts diethyl phthalate and dimethyl phthalate.

13. The method in accordance with claim 1, wherein the thermoplasticmaterial is a vinyl chloride-vinyl acetate copolymer and the plasticizerhas a stabilizer incorporated therein.

14. Apparatus for treating a mass of material in particle form with afluid treating agent comprising a hopper for the mass of particles, aheating jacket surrounding said hopper, said hopper having an opening atthe lower end thereof and an opening near the upper end thereof,a'sleeve communicating with said lower opening, a screw conveyoroperating within said sleeve for conveying particles out of the saidhopper, a tube connecting the said sleeve with the opening at the upperend of the hopper, means for injecting a rapidly moving gaseousconveying medium into the said tube near the connection between the tubeand the sleeve, a nozzle in the said tube slightly upstream from thepoint of injection of the gaseous medium for spraying the fluid treatingagent into the said tube, a source of supply for the fluid treatingagent connected to the said nozzle, a vertical sleeve extending into thehopper open at the lower end and having openings at the upper end,

a baffie surrounding the sleeve located below the said openings, a screwconveyor operating within the vertical sleeve for conveying particlesupwardly from the mass of material and discharging said particlesthrough the said openings against the said bafile, said upper opening inthe said hopper located adjacent the said openings in the verticalsleeve to intermix the particles being discharged through both thehopper opening and the sleeve openings.

15. Apparatus in accordance with claim 14, wherein a second opening isprovided near the top of the hopper for discharge of the said gaseousconveying medium, an upwardly extending housing connected to said secondopening, a filtering means located within the said housing, and conduitmeans connecting the said housing with the said tube for recycling thegaseous conveying medium.

16. Apparatus in accordance with claim 15, wherein a heat exchanger forthe gaseous conveying medium is interposed between the filtering meansand the said tube.

References Cited in the file of this patent UNITED STATES PATENTS664,130 Culmann et al. Dec. 18, 1900 1,386,503 Hulst et al. Aug. 2, 19211,616,547 Pontoppidan Feb. 8, 1927 1,728,411 Howard Sept. 17, 19291,731,953 Thomson Oct. 15, 1929 2,460,546 Stephanoif Feb. 1, 1949

1. THE METHOD OF PLASTICIZING A MASS OF FINELY DIVIDED THERMOPLASTICMATERIAL WHICH INCLUDES THE STEPS OF CONTINUOUSLY REMOVING PARTICLES OFTHE THERMOPLASTIC MATERIAL FROM THE MASS, SUSPENDING THE PARTICLES IN ARAPIDLY MOVING INERT GASEOUS MEDIUM, GRADUALLY SPRAYING THE PLASTICIZERINTO THE SUSPENDED PARTICLES OF THERMOPLASTIC MATERIAL, SEPARATING THETREATED PARTICLES FROM THE GASEOUS MEDIUM AND RETURNING THE TREATEDPARTICLES TO THE MASS.